The present invention relates to a method for forming a fine pattern during manufacturing of a semiconductor.
A method using a chemically amplified resist utilizing chemical amplification which is created by generation of acid is known as a conventional method of forming a pattern, as disclosed by O. Nalamasu et al., Proc. of SPIE, vol. 1466, p. 38 (1991).
In the following, a conventional pattern forming method will be described with reference to FIGS. 13A to 13D.
First, a 2-component material as follows is prepared as a resist material:
______________________________________ Resin which is made alkali-soluble by acid . . . 10 g poly (tert-butyloxycarbonyloxystyrene) (32.5 mol %)- hydroxystyrene 67.5 mol %) Compound which generates acid when under an energy ray 0.5 g (acid generating agent) . . . triphenylsulfoniumtriflate Solvent . . . diethyleneglycol dimethylether 45 g ______________________________________
Next, as shown in FIG. 13A, a semiconductor substrate 1 is coated at its top with the 2-component type resist, and a resist film 2 is formed which has a thickness of 1 .mu.m. Following this, as shown in FIG. 13B, within a cleanroom under a normal condition (ammonia concentration: 15 ppb, humidity: 45%), exposing 4 is performed at 25 mJ/cm.sup.2 on the resist film 2 through a mask 3, using an KrF excimer laser stepper (NA: 0.42).
Next, as shown in FIG. 13C, after performing heating 5 for 90 seconds on the semiconductor substrate 1 at a temperature of 95.degree. C., the resist film 2 is developed for 60 seconds in an alkaline solution of 2.38 wt %, whereby a resist pattern 6 of a positive type is defined as shown in FIG. 13D.
The conventional pattern forming step as above causes the following phenomena on an exposed portion of the resist film 2. That is, a tert-butyloxycarbonyl group included in the resin which is made alkali-soluble by acid which is generated by an acid generating agent during exposing is severed from the resin to thereby cause reaction in which the resin becomes alkali-soluble, and this reaction is promoted during heating and reaches to a bottom portion of the resist film 2. If the resist film 2 is then developed in an alkaline solution, the exposed portion of the resist film 2 dissolves so that the resist pattern 6 of a positive type is obtained.
When a 3-component material as follows is used instead of the 2-component material as above, because of a similar phenomena, a resist pattern of a positive type is formed:
______________________________________ Alkali-soluble resin . . . poly (vinylphenol) 10 g Compound which prevents alkaline dissolution of an 1.5 g alkali-soluble resin and which is made alkali-soluble by acid . . . tert-butyloxycarbonyloxybisphenol A Compound which generates acid when under an energy ray 0.5 g (acid generating agent) . . . triphenylsulfoniumtriflate Solvent . . . diethyleneglycol dimethylether 50 g ______________________________________
This is true with a case where the following commercially available resist materials are used instead of the resist materials as above: APEX-E (Shipley), DX46 (Hoechst), WKR-PT-2 (Wako Pure Chemical), CAMP6 (OCG), ARCH (Fuji Hunt), DP009 (Tokyo Ohka), KRF K2G (Japan Synthetic Rubber) or SEPR (Shin-Etsu Chemical).
However, in the resist pattern 6 which is formed using either one of the resist materials above, acid which is generated by the acid generating agent is deactivated due to an influence of an impurity, such as an amine-contained compound, which is included in an atmosphere, thereby often deteriorating the profile of the resist pattern 6 and hence the resolution of a pattern as shown in FIG. 13D. In short, acid which is generated by the acid generating agent is deactivated due to an impurity, such as ammonia, which usually exists within the cleanroom, and an upper portion of the resist pattern 6 does not become alkali-soluble, whereby an upper portion of the exposed portion of the resist pattern 6 remains even after developed in an alkaline solution.
When etching is performed on a film to be etched, using such a resist pattern having a deteriorated profile, the etched profile of the film to be etched becomes defective and hence a device becomes defective. This deteriorates a yield.
As described above, in addition to ammonia, amine, a substance containing a sulfuric acid ion or an nitric acid ion, etc., are also impurities which deactivate acid which is generated by an acid generating agent.